package audit

import (
	"errors"
	"fmt"
	"sort"
	"strings"

	cid "github.com/TrueCloudLab/frostfs-sdk-go/container/id"
	"go.uber.org/zap"
)

var ErrInvalidIRNode = errors.New("node is not in the inner ring list")

func (ap *Processor) selectContainersToAudit(epoch uint64) ([]cid.ID, error) {
	containers, err := ap.containerClient.List(nil)
	if err != nil {
		return nil, fmt.Errorf("can't get list of containers to start audit: %w", err)
	}

	// consider getting extra information about container complexity from
	// audit contract there
	ap.log.Debug("container listing finished",
		zap.Int("total amount", len(containers)),
	)

	sort.Slice(containers, func(i, j int) bool {
		return strings.Compare(containers[i].EncodeToString(), containers[j].EncodeToString()) < 0
	})

	ind := ap.irList.InnerRingIndex()
	irSize := ap.irList.InnerRingSize()

	if ind < 0 || ind >= irSize {
		return nil, ErrInvalidIRNode
	}

	return Select(containers, epoch, uint64(ind), uint64(irSize)), nil
}

func Select(ids []cid.ID, epoch, index, size uint64) []cid.ID {
	if index >= size {
		return nil
	}

	var a, b uint64

	ln := uint64(len(ids))
	pivot := ln % size
	delta := ln / size

	index = (index + epoch) % size
	if index < pivot {
		a = delta + 1
	} else {
		a = delta
		b = pivot
	}

	from := a*index + b
	to := a*(index+1) + b

	return ids[from:to]
}